In the early stages of heart failure, compensatory mechanisms occur in response to the heart's inability to pump a sufficient amount of blood. One compensatory response is an increase in filling pressure of the heart. The increased filling pressure increases the volume of blood in the heart, allowing the heart to eject a larger volume of blood on each heart beat. Increased filling pressure and other compensatory mechanisms can initially occur without overt heart failure symptoms.
The mechanisms that initially compensate for insufficient cardiac output, however, lead to heart failure decompensation as the heart continues to weaken. The weakened heart can no longer pump effectively causing increased filling pressure to lead to chest congestion (thoracic edema) and heart dilation, which further compromises the heart's pumping function. The patient begins the “vicious cycle” of heart failure which generally leads to hospitalization.
Typically, therapy for a patient hospitalized for acute decompensated heart failure includes early introduction of intravenous infusion of diuretics or vasodilators to clear excess fluid retained by the patient. A new therapy being introduced to remove excess fluid volume from patients with congestive heart failure and/or renal dysfunction is ultrafiltration. Ultrafiltration involves filtering a patient's blood to remove excess fluid then returning the filtered blood back to the patient. Ultrafiltration methods currently in use require manual control of the ultrafiltration unit. A challenge faced in delivering ultrafiltration therapy is knowing when and how much fluid to remove and the rate at which to remove fluid. Removing fluid too quickly may deplete intravascular fluid volume at a rate faster than edematous fluid can be reabsorbed from the tissues. Removing fluid too slowly may allow symptoms and the adverse affects of high filling pressures to persist longer than necessary. If the total fluid volume removed is insufficient, patient symptoms may not be fully alleviated, or alleviated symptoms may return quickly. Overdiuresis can occur if too much fluid is removed. Overdiuresis may require fluid to be administered to the patient to increase the patient's fluid volume status. Removing and adding fluid can pose additional burden on the kidneys, which may already be compromised due to renal insufficiency. A need remains, therefore, for a system and method for use in regulating ultrafiltration therapy.